1. 2.4 Chemical Reactions Notes

2. Chemical Reactions
A process that changes one set of chemicals into another set of chemicals
Can happen quickly or slowly
Reactants  what you start with
Elements or compounds that enter in to a chemical reaction
Products  what you end with
Elements or compounds produced
from a chemical reaction

3. Chemical Reactions
Chemical equations use symbols and formula to represent reactants and products
Arrow means “yields” and shows the direction of the reaction:
reactants to products 2H2 + O H2O
Reactants
yields
Products

4. Chemical Reactions
Chemical bonds are being broken and formed during a chemical reaction
Law of Conservation of Matter  atoms are not created nor destroyed but are REARRANGED!
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5. Energy in Reactions
Chemical reactions always involve changes in energy
Exothermic reaction  energy is released (burning paper; cellular respiration)
Energy released can be in the form of heat, sound or light
Endothermic reaction  energy is absorbed (baking; photosynthesis )

6. Energy in Reactions
The flow of energy determines if a reaction will occur
If energy is released, the reaction often occurs spontaneously
Reactions that are not spontaneous require an input of energy

7. Energy-Absorbing Reaction Energy-Releasing Reaction
Products
Activation
energy
Activation energy
Reactants
Reactants
Products
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8. Activation Energy Energy needed to start a reaction
Some reactions have a high activation energy while others have low activation energy
Often reactions require too much energy.
Living things reduce the amount of energy needed by using catalysts
A catalyst speeds up a reaction by lowering activation energy

9. Catalysts EA = Activation Energy enzyme enzyme EA without EA with
LE 5-5b
Catalysts
EA = Activation Energy
EA without
enzyme
EA with
enzyme
Reactants
Energy
Net
change
in energy
Products
Progress of the reaction
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10. Enzymes Proteins that act as biological catalysts
Cells use enzymes to speed up chemical reactions that take place in the cell
Are very specific  they catalyze only one reaction

11. How do enzymes work? Work like a lock and key
Enzymes have an active site that binds to the reactant (substrate)
Once bound, the enzyme changes the reactant to some product 12

12. Enzyme (hexokinase) Substrates Products Active site Glucose ADP ATP
phosphate
ATP
Products
are released
Active site
Enzyme-substrate
complex
Substrates
bind to
enzyme
Substrates
are converted
into products
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13. Enzyme (hexokinase) Substrates Products Active site Glucose ADP ATP
phosphate
ATP
Products
are released
Active site
Enzyme-substrate
complex
Substrates
bind to
enzyme
Substrates
are converted
into products
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14. Enzyme (hexokinase) Substrates Products Active site Glucose ADP ATP
phosphate
ATP
Products
are released
Active site
Enzyme-substrate
complex
Substrates
bind to
enzyme
Substrates
are converted
into products
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15. Enzyme (hexokinase) Substrates Products Active site Glucose ADP ATP
phosphate
ATP
Products
are released
Active site
Enzyme-substrate
complex
Substrates
bind to
enzyme
Substrates
are converted
into products
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16. Regulation of Enzyme Activity
Many things affect the rate of enzyme activity in the cell pH
Temperature
Other molecules
Enzyme activity can be turned on or off at certain stages depending on what the cell needs